The present invention relates to a chemical looping deoxygenation (CLDO) process for deoxygenating the flue gas resulting from oxy-fuel combustion reactions.
Combustion boilers for the generation of steam or electricity are operated in excess oxygen mode. The objective of this excess oxidizer is to ensure complete combustion of the fuel in order to achieve high efficiency of the plant and to obtain a low content of carbon compounds in the ash, thus enabling the ash to be utilized. The usual oxygen content in the flue gas at the outlet of the boiler is generally 2 or 3% by volume (on a dry basis).
For oxy-fuel combustion boilers intended for CO2 capture, the operating mode is the same. However, there is the additional constraint of a limit to the oxygen content in the CO2 produced. This is because, for EOR (enhanced oil recovery) applications, the oxygen is reputed to have negative effects on the point of injection into the reservoir (overheating of the injection point by an exothermic reaction with the oil) and on the redox conditions of the reservoir. EOR enables the useful lifetime of oil production fields to be extended and stands out as the most promising shorter-term application for storing very large quantities of captured CO2.
In the context of the European project ENCAP, the limit set for this oxygen content in the case of EOR applications is 100 ppmv. For simple CO2 storage, typically in deep aquifers, the oxygen is incorporated into a mass of inerts. The upper limit of these inerts is 4% by volume.
Among the several existing processes for limiting the presence of O2 in oxy-fuel combustion flue gas are in particular the following: the inert separation process; the catalytic combustion process; the adsorption process; and, finally, the chemical looping combustion (CLC) process. Of these techniques, the process best suited to the intended objective is that of catalytic combustion. However, this process has several drawbacks:                high consumption of fuel (hydrogen);        usually accepted O2 content as upper limit of 1.5% by volume; and        risk of contaminating the catalyst (noble metals) by compounds resulting from the combustion of fossil fuels (coal/biomass/residues, etc.).        